Memory-lite

Japanese pack a terabyte into a sugarcube

It sounds like Star Trek or an Iain Banks novel, but it's real. Japanese scientists have managed to pack a terabyte (1,000GB) of data into a 1cm cube.

A marketable device that can use this technology may already be in sight, engineers and scientists from Kyoto University and manufacturer Central Glass said on Tuesday.

The scientific group, which holds patents on the technology, is almost ready to start working on its commercial development according to Professor Kazuyuki Hirao of the department of material chemistry at Kyoto's Graduate School of Engineering. Hirao said such work would begin before the end of the year.

About two years ago the group discovered that a very short light pulse produced by a femtosecond laser can transform glass containing the rare element samarium. It makes a dot around 400 nanometres in diameter become luminous while the rest of the glass remains transparent. This difference allows the glass to be used as an optical memory.

These luminous dots can be spaced 100 nanometres apart on a glass surface that includes samarium. The group has now confirmed these dotted surfaces can be layered.

The Japanese scientists found that the equivalent of 2,000 layers of dots in a cubic centimetre of glass were able to store the equivalent of eight terabits of data (eight terabits is one terabyte or 1,000 gigabytes), according to Shigeki Sakaguchi at the fine chemical business planning division of Central Glass.

"By irradiating with a femtosecond laser and changing the number of elements we discovered that it is possible to read each layer as individual data," said Kyoto University's Hirao, who specialises in femtosecond lasers.

A femtosecond laser irradiates for just a 1,000-trillionth of a second. The study into the possibility of using glass as an optical storage medium was started in 1994. But the study group only discovered about two years ago that such lasers are necessary because longer pulses of light cause excessive heat.

"If a nanosecond or picosecond laser is applied on glass, the radiated heat causes glass to crack. Only a femtosecond laser can irradiate without heat," Hirao said.

Hirao said femtosecond lasers are the only ones able to cut a molecule. Hirao is also working on a broadband communication technology project in which femtosecond lasers enable the transmission of terabits of data per second.

Holographic memory, another three-dimensional medium, has been around for more than 20 years but its structure is so complex that it is not yet possible for it to be developed as a practical memory device, according to Central Glass' Sakaguchi.